1. Field of the Invention
This invention relates to aircraft and more particularly to aircraft having a pair of counter rotating rotors.
Aircraft of this type are generally known in the form of helicopters. Helicopters have several severe disadvantages which limit their field of application substantially. The axis of their rotors e.g. needs to be located near the center (of gravity) of the helicopter which reduces the useful volume of the cabin. The complexity of control of helicopters requires expensive and extensive training of pilots. The speed in horizontal flight is limited by non symmetric relative air flow velocity at the rotor blades causing changing mechanical forces on the blades. The free blades are often a source of accidents, since every contact of the rotor blades with other objects results in an extremely dangerous situation for the aircraft.
2. Description of the Prior Art
Therefore, based on the general principle of helicopters it has been tried to avoid these disadvantages by enclosing the rotors partly or completely into a housing. Aircrafts of this type are disclosed in Swiss Patent Specification No. 558 737, in Australian Patent Specification No. 474 805 and in U.S. Pat. Nos. 2,777,649, 2,395,876 and 2,461,435. For controlling these aircrafts in flight, air directors are provided in the air stream of the rotors. By means of these air directors, the rotor stream is guided and deflected especially for horizontal flight. Therefore, the air directors or blades substantially extend in a transverse direction to the flight direction of the aircraft. For the hovering flight, however, the disclosed air director systems are not suited, since they do not allow the control of the aircrafts along all axes in space in the hovering flight. Especially, translational movements along all horizontal directions can not be controlled with the known systems in the hovering phase. Moreover, the control of these aircrafts is complicated because horizontal and vertical forces derived from the rotor stream in the hovering flight are in complex interdependence. Therefore, difficulties will arise in maneuvering and controlling these aircrafts.